Firebug is always just a keystroke away, but it never gets in your way. You can open Firebug in a separate window, or as a bar at the bottom of your browser. Firebug also gives you fine-grained control over which websites you want to enable it for. More Info »
Firebug makes it simple to find HTML elements buried deep in the page. Once youve found what youre looking for, Firebug gives you a wealth of information, and lets you edit the HTML live.